Insulin-like Growth Factor I (IGF-I) is a peptide present in plasma and other body fluids. It comprises 70 amino acids, including 3 disulphide bonds, and can stimulate growth of a wide range of cell types and it mediates the effects of growth hormone on skeletal growth. Human IGF-I has been purified from plasma and its complete amino acid sequence is established. Sequences with extensive homologies to human IGF-I are present in IGF-I purified from plasma of other species. IGF-I has both systemic and local effects and appears mostly associated with different specific binding proteins, four of which have been sequenced and are termed IGFBP1, IGFBP2, IGFBP3 and IGFBP4. These appear to modulate the biological functions and availability of IGF-I in both positive and negative manners. Analogues with changed affinities for the binding proteins have been produced and changes of biological activities related to sequence variation have been found. IGF-I appears to act mainly by interactions with the IGF-type 1 receptor exposed on the outer surface of plasma membranes in many different cell types. However, binding to IGF type 2- and insulin receptors also seems to be of importance. Because of the scarcity of purified plasma IGF-I there was a great necessity to develop methodology for the commercial scale production of IGF-I. Nowadays, such large scale production can readily be achieved by using recombinant DNA techniques. As a result of studies with preparations of recombinant IGF-I (rIGF-I), it has been demonstrated that rIGF-I promotes skeletal growth and skeletal muscle protein synthesis. Moreover, IGF-I is also effective for the treatment or prevention of catabolic states in patients (Swedish patent application SE 9002731-9) and improves the regeneration of transected periferal nerves (EP 0 308 386). It has previously been demonstrated in vitro that IGF-I also can promote actin synthesis in myocytes in culture (Florini, J. R., Muscle and Nerve 10 (1987)577-598) and contractility of neonatal rat cardiocytes in vitro (Vetter, U et al., Basic Res. Cardiol. 83 (1988)647-654). Prior art has, however, not extended these observations to the whole animal or to therapeutic usefulness.